Laminated electronic components such as laminated ceramic capacitors are widely used as compact, large-capacity and highly reliable electronic components. As devices have become more compact and higher performing in recent years, there has been an increasingly strong demand for further miniaturization, increased capacity, lower cost and greater reliability in electronic components and especially in laminated electronic components such as laminated ceramic capacitors.
Laminated ceramic capacitors are normally produced by laminating a paste for internal electrode layers and a paste for dielectric layers using a sheet process or a printing process etc., and then simultaneously baking the internal electrode layers and the dielectric layers in the laminated body.
A barium titanate-based dielectric composition comprising barium titanate as the main component which has a high dielectric constant is conventionally widely known as a dielectric composition which is used for the dielectric layer. There is a problem with a barium titanate-based dielectric composition, however, in that the insulation resistance thereof deteriorates markedly at high temperatures of 100° C. or above.
Furthermore, a capacitor may be used with a DC voltage superimposed on an AC voltage. The DC bias characteristics are important when a capacitor is used with a DC voltage superimposed on an AC voltage. The DC bias characteristics express a change in the dielectric constant which is dependent on application of a DC voltage. The DC bias characteristics are higher the smaller the change in the dielectric constant with respect to application of a DC voltage. It is known that a capacitor employing a conventional barium titanate-based dielectric composition has low DC bias characteristics, and the greater the DC voltage, the lower the dielectric constant.
In addition, when the dielectric layer is made thinner in order to make the laminated ceramic capacitor more compact and to increase the capacity thereof, the electric field applied to the dielectric layer becomes more intense when a DC voltage is applied, so there is a further drop in the DC bias characteristics.
Furthermore, Pd or Pd alloy is generally used as the conductive material of the internal electrode layers in the laminated ceramic capacitor. However, Pd is costly so in recent years use has also been made of relatively inexpensive base metals such as Ni and Cu.
When a base metal such as Ni or Cu is used as the conductive material of the internal electrode layer, the internal electrode layer oxidizes when baking is carried out under the atmosphere. This means that it is necessary for the dielectric layer and the internal electrode layer to be simultaneously baked under a reducing atmosphere. When baking is carried out under a reducing atmosphere, however, the dielectric layer is reduced and there is a drop in insulation resistance.
In view of this, there is a need for a non-reducing dielectric composition which has excellent DC bias characteristics and has high insulation resistance at high temperatures.
As a means for resolving this situation, for example, Japanese Patent JP 3334607 describes a laminated ceramic capacitor which has good DC bias characteristics and high insulation resistance at high temperatures, and a barium titanate-based dielectric composition which is suitable for the laminated ceramic capacitor.
However, although the dielectric constant of the dielectric composition in Patent Japanese Patent JP 3334607 is relatively high at around 900-950 when a DC electric field of 5 V/μm is applied, the dielectric constant decreases when an even higher DC electric field is applied, so the DC bias characteristics are inadequate to cope with the thinning of the layers which accompanies a reduction in size and increased capacity.
Furthermore, the dielectric composition in Japanese Patent JP 3334607 has relatively high insulation resistance at a high temperature of 150° C. However, this is still inadequate in comparison with the magnitude of insulation resistance required in recent years.